The present invention relates to seamed joints, namely for packagings with a top and a bottom assembled by seaming, and in particular to seamed joints of this type for metallic drums or the like. The joints are of the kind in which the adjacent edges of the body and of the bottom form generally alternating layers of an intermixed structure extending a certain height in an axial direction. The seams, called simple, double and triple, are well known and respectively consist of three, five and seven layers of the material. The double and the triple seams correspond to the most currently used technical processes in the manufacturing of metallic drums or composite drums.
The seam is often the zone or area of a package or container which is most exposed to dislocation, particularly in the case of an accidental drop. Consequently, means and ways of improving the mechanical resistance or strength of this kind of joint have been investigated for a long time.
As far back as 1919 (see British Pat. No. 142.967), a process directed to the reinforcement of a seamed joint has been described. That process consists of overfolding the edge of the bottom on itself so as to bring it in overthickness during seaming. After that operation, the seaming was performed in such a way that the adjoining parts of the bottom and of the body are present to form a bending of the seam structure along its height.
Belgian Pat. No. 793 875 describes the use of such a process applied to double seamings and points out that the overfolding may be made either on the edge of the bottom, or on the edge of the body of a metallic drum or the like.
That kind of process leads to structures of assembled joints, which are confined between two limiting surfaces of which at least one presents a bending of an amplitude corresponding roughly to the overwidth formed by the previous overfolding of one of the assembled parts. If, for instance, the profile of the outside surface of the joint is kept and maintained practically straight, the result is that the profile of the inside surface of the joint will be bent or curved. This imposes a sinuous shape or course in the internal structure of the joint which will mainly affect the layer or the layers located between the inside surface of the joint and the overfolded layer which causes the overthickness.
A seam structure made in that way improves the mechanical performances of the joint in certain situations. Experience shows, nevertheless, that this improvement remains limited, namely owing to the fact that the amplitude of the bending is restricted to the overthickness created by the thickness of the body itself.
French Pat. No. 1,447,436 and the first additional certificate No. 89 175, describe a technical process for the assembly of a bottom upon the body of a container leading to a bonding seam consisting of more than five thicknesses of steal sheet, namely a triple seam with seven thicknesses of steal sheet. That process is essentially characterized by the fact that the radial edge of the bottom is pushed back before the edge of the body is pushed back. This causes the bottom edge to wind along and around the body edge.
French Pat. No. 7523885 describes a development of that triple seam process consisting essentially of a preparation procedure for the bottom edge. Prior to rolling the two edges around one another, the peripheral zone of the bottom edge is bent a predetermined angle in the direction of the body edge and a small, open hook is formed in that peripheral zone, with the open side of that hook facing the axis of the drum body.